Pneumatic concentric nebuliser

The microconcentric nebuliser (MCN) is another low-flow concentric pneumatic nebuliser designed to analyse low-volume samples. In contrast to the DIN and the HEN, the MCN is capable of nebulising samples containing high concentrations of mineral acids (e.g. hydrofluoric... 

The extension of inductively coupled plasma (ICP) atomic emission spectrometry to seawater analysis has been slow for two major reasons. The first is that the concentrations of almost all trace metals of interest are 1 xg/l or less, below detection limits attainable with conventional pneumatic nebulisation. The second is that the seawater matrix, with some 3.5% dissolved solids, is not compatible with most of the sample introduction systems used with ICP. Thus direct multielemental trace analysis of seawater by ICP-AES is impractical, at least with pneumatic nebulisation. In view of this, a number of alternative strategies can be considered ... 

In order to overcome drawback 1 several nebulisers and spray chambers have been developed. In this field, considerable effort has been dedicated to the design of new pneumatic devices able to efficiently take advantage of the gas kinetic energy. To solve drawback 2, two general choices are available (i) pneumatic concentric nebulisers with modified critical dimensions and (ii) pneumatic nebulisers in which the geometry of the liquid and gas interaction is not concentric. Other non-pneumatic nebulisers have also been designed that overcome either or both of these drawbacks. 

A pneumatic cross-flow micronebuliser has been described for use in ICP-MS. The high efficiency cross-flow micronebuliser (HECFMN) has a narrow capillary placed inside the conventional sample capillary. The inner diameter of the nebuliser gas nozzle is reduced with respect to the conventional cross-flow design. Due to the characteristics of this device, the free liquid uptake rate (i.e. about 9 p-L/min) is lower than that found for either a conventional cross-flow nebuliser (i.e. 1900 pL/min) or concentric pneumatic micronebulisers (i.e. from about 30 to 100 pL/min). This fact makes the HECFMN attractive for CE ICP-MS interfaces. ... 

With the standard sample introduction system, consisting of a pneumatic nebuliser and spray chamber, only droplets < 10 xm in diameter are permitted to reach the ICP. This selection results in an analyte introduction efficiency of only 1-2%, but is required to maintain plasma stability and ensure efficient desolvation, atomisation and ionisation in the ICP. Additionally, the total concentration of dissolved solids is usually limited to a maximum of 2 g/L only, to prevent clogging of the nebuliser, torch injector tube and/or sampling cone and skimmer orifices, and also to limit signal suppression and long-lasting memory effects. Of course, when using ETV for sample... 

Another low-flow nebuliser used for coupling ICP-MS to chromatographic columns is the high-efficiency nebuliser (HEN). This device has a small capillary and is used with a spray chamber. Compared to pneumatic nebulisers, the HEN operates more efficiently at very low solution uptake rates. Micro-HPLC-HEN-ICP-MS coupling was applied to the speciation of five arsenic compounds. The HEN operated most efficiently at sample uptake rates of 40 pL/min and was shown to have excellent absolute detection limits. A possible drawback of the HEN, as for all low-flow nebulisers, is the poor tolerance in nebuhsing highly concentrated solutions. 

Pneumatic Concentric Nebuliser. The current design of the pneumatic concentric nebuliser is probably the most common type used. It consists of a concentric glass through which a capillary tube is fitted. The sample is drawn up from the spray... 

Figure 2.9 Overview of sample introduction methods and hyphenated techniques used in ICP-AES. (A) Pneumatic concentric (sometimes called the Meinhard nebuliser) (B) Babington (C) fritted disc (D) Hildebrand nebuliser (E) cross flow (G) standard ultrasonic nebuliser for aqueous and non-aqueous solvents (H) electro-thermal graphite ( ) electro-thermal carbon cup (K) graphite tip filament (L) laser ablation (M) hydride generation (P) flow injection...

Generally, a liquid sample introduction system suitable for ICP-MS consists of two main components (i) a nebuliser that turns the liquid bulk into an aerosol and (ii) a spray chamber that selects the maximum drop size that will be introduced into the plasma. The most often used nebuliser-spray chamber combination for ICP-MS is depicted in Figure 5.1. It consists of a pneumatic concentric nebuliser coupled to a double pass spray chamber. 

The dimensions of pneumatic concentric nebulisers play a very important role in terms of their applicability to the analysis of complex samples. Figure 5.2 shows several different concentric nebulisers with varying performance properties. While nebuUser (a) suffers from tip blocking when introducing high salt content solutions and slurries, nebuUser (b) is able to work with 20% sodium chloride solutions. NebuUser (c) works properly witU slurries having soUd particles... 

Figure 5.2 Pictures of several glass pneumatic concentric nebulisers. (a) Conventional nebuliser (b) nebuliser suitable for the analysis of high salt content solutions (c) nebuliser suitable for the analysis of slurries (d) nebuliser used for the introduction of very small samples (e) nebuliser (b) operated with deionised water (f) nebuliser (c) operated with deionised water and (g) main dimensions of each nebuliser.

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